Description: The planktonic foraminifer Globigerinoides sacculifer (Brady) was maintained in the laboratory under different temperature (19.5-29.5°C) and salinity (33 and 36‰) regimes. The light and feeding conditions were adjusted to the open ocean environment. The light intensity and quality corresponded to a water depth of 10-30 m and the specimens were fed daily. Specimens were raised from a mean initial size of approximately 220-240 μm to the reproductive mean size ranging from 521 μm to 657 μm according to the different temperature and salinity regimes. The survival time decreased with increasing temperature relatively independent of salinity. The growth rate decreased with decreasing temperatures but significantly only at the lowermost temperature range. The general vitality increased with increasing salinity, partially indicated by more chamber formations of specimens of the 36‰ salinity group in comparison to those of the 33‰ salinity group. The different phenotypes of the final chamber and the different morphologies of G. sacculifer are discussed.

Description: We critically evaluate the applicability of Ca-isotope ratios in planktonic foraminifers as proxy for past sea surface temperatures (SST) and isotope composition of paleo-seawater (δ44Casw) reconstructions. Previous studies have shown discrepancies regarding the temperature sensitivity of Ca isotope fractionation in foraminifers of more than one order of magnitude. We present new data from the planktonic foraminifer species Orbulina universa, Globigerinoides sacculifer and Neogloboquadrina pachyderma (sinistral) from culture experiments, multinet deployments and coretop samples. Specimens of G. sacculifer cultured at low salinities (33–34.5) show predominantly no major temperature dependent Ca isotope fractionation, in contrast to previous individuals cultured at higher salinities of 34.5–36. The new data of O. universa are consistent with previously published results, revealing a small but significant temperature sensitivity. Calcium isotope fractionation in tests of N. pachyderma shows a significant variation with temperature, which is not uniform over the total investigated temperature range (−1.6 °C to +10 °C), possibly reflecting the influence of additional controlling factors besides temperature. Controlled dissolution experiments in the laboratory indicate that the Ca-isotope composition of G. sacculifer and N. pachyderma is relatively insensitive to partial dissolution of their tests. Calcium isotope ratios in the planktonic foraminifers G. sacculifer and N. pachyderma (s) reveal a complex Ca isotope fractionation behaviour, which is not yet fully understood. Additional validation studies are crucial to enhance the basic understanding of the calcium isotope systematics in planktic foraminifer shells, and the potential for applying Ca-isotope ratios as proxies for seawater temperature and the oceanic Ca budget.